Stewardship and management of freshwater ecosystems: From Leopold's land ethic to a freshwater ethic

1. In 1949, Aldo Leopold formalized the concept of the ‘land ethic’, in what emerged as a foundational and transformational way of thinking about natural resource management, biodiversity conservation, and stewardship in terrestrial systems. Yet, the land ethic has inherent linkages to aquatic ecosystems; Leopold himself conducted research on rivers and lakes, and freshwater ecosystems figured widely in his writing.
2. We reflect on the land ethic and other aspects of Leopold's scholarship to identify key messages that provide insight into the stewardship and management of freshwater ecosystems around the globe. We also frame what we call the ‘freshwater ethic’ around Leopold's legacy. Although Leopold could not have envisaged the stressors affecting modern aquatic ecosystems, his core principles remain salient. These apply not only to ecosystem protection, but also to the ethics of modern conservation economics, sustainability, and the protection of natural capital, in which lakes, rivers, and wetlands now figure prominently.
3. We identify key ‘Aldo-inspired’ recommendations for protecting and restoring freshwater ecosystems in the Anthropocene that emanate directly from his writings (e.g. adopt an ecosystem approach, identify win–win–win scenarios, recognize the irreplaceability of wild waters, and strive for freshwater optimism).
4. In an epoch where links between people and nature are becoming more explicit in environmental management, policy, and governance, we suggest that Aldo Leopold's work illustrates how inspirational, seminal thinkers have offered leadership in this domain. We contend that today there is still much that can be learned from Leopold, especially by the next generation of environmental practitioners, to ensure the effective stewardship of our aquatic ecosystems.
5. We submit that the adoption of a freshwater ethic in parallel with Leopold's land ethic will enhance the stewardship of the world's increasingly threatened fresh waters by raising the profile of the plight of fresh waters and identifying enduring actions that, if embraced, will help conserve and restore biodiversity.

     

The aetiology of spinal deformity in Atlantic salmon, Salmo salar L.: influence of genetic factors on the frequency and severity in freshwater stages

A radiographic study was carried out on 2-year groups of pre-smolt parr to detect the comparative frequency of vertebral change in a range of defined pedigreed families of high growth rate of Atlantic salmon, Salmo salar L., reared under identical conditions. The observed frequency of deformity was related to the observed deformity level in the seawater parental generation, and to a potentially uncontrolled environmental determinant, i.e. stripping date. High and low parental deformity groups of families were found to produce offspring that had very similar levels of radiographically detectable spinal deformities in the pre-smolt parr, suggesting no genetic link. With regard to stripping date, the overall incidence was nearly half that seen in the preceding year (8.7% cf 16.6%). However, a non-significant trend to fewer radiographic spinal deformities was seen in the later stripping period.     

Flow-field observations of a tidally driven island wake used by marine mammals in the Bay of Fundy, Canada

Correlations between fine‐scale oceanographic features and aggregations of marine mammals are frequently reported, but the physical forces shaping these relationships are rarely explored. We conducted a series of oceanographic observations and remote sensing surveys of an oceanographic feature near Grand Manan Island known to attract marine mammals on flood tides. We tracked drift drogues from cliff‐top with a theodolite and conducted box‐type surveys with an acoustic Doppler current profiler (ADCP) to assess flow patterns within the oceanographic feature. The feature was also visualized with Synthetic Aperture Radar (SAR) scenes. Drift drogues were advected towards a shear line originating near the northern tip of the island and entrained in one or more eddies downstream. ADCP surveys confirmed the presence of the shear line between rapid easterly flow and slower return flow. As the tide progressed, the shear line extended and manifested a single anti‐cyclonic eddy at its distal end. As the flood tide progressed, northerly flow along the eastern shore of the island intensified and deflected the shear line northwards, shedding the eddy at slack high water. SAR images confirmed the presence of the shearline and eddy system, illustrating the evolution of a wake behind the island on flood tides. Profiles of flow direction and acoustic backscatter revealed secondary flows within the wake consistent with models and observations of other wakes. Oceanographic and remote sensing observations confirm that an island wake is generated by tidal flow past Grand Manan Island and provide an ecological context for the predictable aggregations of odontocete and mysticete cetaceans observed foraging within this region.     

Naturally occurring bacteraemia in American lobsters, Homarus americanus Milne-Edwards, in Long Island Sound

The health status of the American lobster, Homarus americanus Milne-Edwards, in Long Island Sound (LIS) has been in decline, with seasonal mortality events occurring since 1998. In order to assess the potential effects of environmental conditions on lobster health via haemolymph analysis, lobsters collected from various sites in LIS were examined and sampled while concurrent environmental data (water temperature, salinity and dissolved oxygen) were recorded. The pH of the haemolymph of each lobster was tested, followed by a collection of haemolymph for serum biochemistry analysis and bacterial culture. This report focuses on the results of the bacterial sampling. The majority of bacteria cultured were opportunistic pathogens commonly found in the environment, including some that are associated with sewage and pollution. The prevalence of bacteraemia was correlated with the site of collection, the month in which the lobsters were sampled, and water temperature.     

Long-term patterns of microhabitat use by fish in a southern Appalachian stream from 1983 to 1992: effects of hydrologic period, season and fish length

Abstract— We quantified microhabitat use by members of a southern Appalachian stream fish assemblage over a ten-year period that included both floods and droughts. Our study site (37 m in length) encompassed riffle, run and pool habitats. Previous research indicated that species belonged to either benthic or water-column microhabitat guilds. Most species exhibited non-random microhabitat use in all seasons, and benthic and water column species generally were over-represented in the deeper portions of the site. In addition, water column species generally were over-represented in microhabitats with lower average velocities. The majority of seasonal shifts in microhabitat use were passive (i. e. correlated with changes in microhabitat availability), whereas, most shifts associated with hydrological periods appeared to be active responses to changing environmental conditions. Most species exhibited length-related shifts in microhabitat use, which were strongly affected by hydrologic period for four of ten species. Microhabitat use patterns of assemblage members appeared to be a consequence of species-specific responses to changing environmental conditions. The highly flexible patterns of microhabitat use exhibited by these species necessitate that decisions regarding their management be based on data covering a range of environmental conditions.     

Marine temperatures experienced by postsmolts and the survival of Atlantic salmon, Salmo salar L., in the North Sea area

The survival of two Atlantic salmon stocks that inhabit rivers confluent with the North Sea was examined in respect to historical distributions of sea surface water temperatures. The rivers Figgjo and North Esk are relatively small salmon rivers in southern Norway and eastern Scotland, respectively. Wild salmon smolts have been tagged in these rivers since 1965. Tag returns were used to evaluate the survival of salmon in the North Sea. Survival rates of one-sea-winter (1SW) and 2SW fish were correlated within stocks, as well as between stocks. Survival rates were compared with the areal extent of thermal habitat in the north-eastern Atlantic Ocean. A positive correlation was found between the area of 8–10°C water in May and the survival of salmon. A reciprocal negative correlation was also found between survival and 5–7°C water in the same month. An analysis of sea surface temperature distributions for periods of good vs. poor salmon survival showed that when cool surface waters dominate the Norwegian coast and North Sea during May, salmon survival has been poor. Conversely, when the 8°C isotherm has extended northward along the Norwegian coast during May, survival has been good. The effect of water temperature distributions on the growth of postsmolts and other survival factors are discussed.     

Influence of dietary palm oil on growth, tissue fatty acid compositions, and fatty acid metabolism in liver and intestine in rainbow trout (Oncorhynchus mykiss)

This study aimed to investigate the effects of dietary crude palm oil (CPO) on fatty acid metabolism in liver and intestine of rainbow trout. Triplicate groups of rainbow trout for 10 weeks at 13 °C were fed on diets in which CPO replaced fish oil (FO) in a graded manner (0–100%). At the end of the trial, fatty acid compositions of flesh, liver and pyloric caeca were determined and highly unsaturated fatty acid (HUFA) synthesis and fatty acid oxidation were estimated in isolated hepatocytes and caecal enterocytes using [1‐¹⁴C]18:3n‐3 as substrate. Growth performance and feed efficiency were unaffected by dietary CPO. Fatty acid compositions of selected tissues reflected the dietary fatty acid composition with increasing CPO resulting in increased proportions of 18:1n‐9 and 18:2n‐6 and decreased proportions of n‐3HUFA, 20:5n‐3 and 22:6n‐3. Palmitic acid, 16:0, was also increased in flesh and pyloric caeca, but not in liver. The capacity of HUFA synthesis from 18:3n‐3 increased by up to threefold in both hepatocytes and enterocytes in response to graded increases in dietary CPO. In contrast, oxidation of 18:3n‐3 was unaffected by dietary CPO in hepatocytes and reduced by high levels of dietary CPO in enterocytes. The results of this study suggest that CPO can be used at least to partially replace FO in diets for rainbow trout in terms of permitting similar growth and feed conversion, and having no major detrimental effects on lipid and fatty acid metabolism, although flesh fatty acid compositions are significantly affected at an inclusion level above 50%, with n‐3HUFA reduced by up to 40%.     

Mathematical simulation and calculation of the soil compaction under dynamic loads

The deformation and compaction of loamy sandy soddy-podzolic soils under linear dynamic changes in the compressive stresses and in the course of the soil creeping were studied in field experiments. The rheological properties of these soils occurring in the viscoelastic state were described by a first-order differential equation relating the compressive stresses, the rates of their changes, and the velocities of the relative vertical compressive deformation. Regression equations were derived for the viscoelastic properties of the studied soil as functions of its density, moisture, and linear compaction velocity. Methods were proposed for the calculation of indices of the stress-strain state and the compaction of soils under specified conditions of changes in their compressive stresses with time and in the course of the soil creeping after the initial linear increase in load. Corresponding computer programs were developed. The effect of the main factors due to the linear increase in the compressive loads and in the course of the soil creeping on the rheological properties, the stress-strain state, and the density of soils was quantitatively estimated. The calculation showed that the values of the soil deformation and the density under compressive stresses lower than the ultimate strength were stabilized with time, and the properties of the viscoelastic soil approached elastic ones.     

Application of biochar to soil and N2O emissions: potential effects of blending fast‐pyrolysis biochar with anaerobically digested slurry

Soil applications of recalcitrant biochar offer the possibility of mitigating climate change effects through long‐term carbon sequestration and potentially also by reducing emissions of the potent greenhouse gas nitrous oxide (N₂O). This laboratory study examined the effect of combining a fast‐pyrolysis biochar at small (1% by mass) and large (3%) concentrations with anaerobically digested slurry on soil N₂O and carbon dioxide (CO₂) emissions over a period of 55 days. The results showed that fast‐pyrolysis biochar applied on its own increased N₂O emissions from soil. However, when biochar was applied together with slurry, the larger biochar concentration decreased N₂O emissions by 47%, relative to those from the slurry treatment with the smaller biochar concentration. Reduced N₂O emissions coincided with enhanced soil microbial activity and immobilization of nitrogen. A combined application of biochar and anaerobic digested slurry could therefore be beneficial for cropping systems in terms of soil nitrogen retention while concurrently mitigating N₂O fluxes and sequestering carbon in soil.